Carburetor

ABSTRACT

A carburetor capable of suitably controlling the fuel flow rate over the entire operational range of the associated engine using a three-dimensional-type fluidic device.

United States Patent Hohsho et a]. 14 1 June 13, 1972 [54] CARBURETOR[56] References Cited [72] Inventors: Yukio Hohsho, Katsuta; KoichiroYamlda, UNITED STATES PATENTS Yfishishlgfe Q Hitachp 3,389,894 6/l968Binder ..26l/D1G. 69 Tim Tmnlshh 3,574,346 4/1971 $611611 ...26|/D|G. 69Hlwchl- 011111111" 3,392,739 7/1968 Taplin et a1. ...26l/DIG. 69 [73]Assignce; Hitachi Ltd 'f k Japan 3,541,865 11/1970 Brown ..137/81.53,361,416 H1968 Morgan et a1.. ..26l/69 R I 1 FllcdI -y I970 3,577,9645/1971 Lazar ...26l/D1G. 69 [2 I] AbpL 39,076 3,386,709 6/1968Drayer.... ...'261/1)1o. 69 3,477,699 1 H1969 Drayer.... ...261/D1G. 693,548,795 12 1970 Howland..... ...26I/D|G. 69 1 Foreign ApplicationPrwmy Dam 3,544,082 12/1970 Fort et a1. ..26l/D1G. 69

May 21, 1969 Japan ..44/38734 1 Primary Examiner-Tm R. MllesAttorney-Craig, Antonelli & Hill [52] U.S. C1. ..261/36 A, 261/69 R,137/8l.5,

l23/9R [57] ABSTRACT 1 [lilt- A arburetor capable of suitably onnuinsthe fuel flow ale Fleld Search-m 251/1316- 69,3644, R; over the entireoperational range'of the associated engine FUR TANK using athree-dimensional-type fluidic device.

5 Claim, 7 Drawing Figures PATENTEDJUN 1 3 m2 SHEET 2 BF 3 L FUEL TANKFIG 5 INVENTORS YU/(ID Hays/m, m/m/Ro mmw,

ATTORNEYS CARBURETOR BACKGROUND OF THE INVENTION Presently, varioustypes of carburetor are being used but, on the other hand, therequirements for carburetor characteristics are becoming complicatedmore and more with an increasing demand for higher engine performanceand an increasing demand for counter-measures for the exhaust gasproblem, and these requirements are too complicated to be met by theconstructions of the presently used carburetors. On the other hand, theaddition of various supplementary devices to meet such requirementscreates an economical problem. Then, it can be considered to satisfy theaforesaid requirements by applying to a carburetor a fluidic logicaldevice which has been developed as means for precisely controlling theflow rate of fluid.

The fluidic logical devices presently being used for practicalapplications are mostly of pseudo-two dimensions. Namely, they are ofthe type wherein fluid passages are fonned by providing grooves betweenflat plates and a control pressure is acted at the branched portionthrough a control passage. However, in such type of fluidic logicaldevice wherein fluid is confined within two dimensional planes, when aliquid is used as a fluid to be controlled, a divergent current of theliquid flowing along the wall surface of the channel on this side of thebranched portion is relatively large in quantity during operation and aprecise fluid control can hardly be obtained when the value of controlpressure is small. In addition, if a high negative pressure acts on thecontrol pipe, the divergent current is sucked into said control pipe andthe liquid is accumulated within the control pipe, providing a cause ofhysteresis and causing an irregularity in flow control.

Besides the type described above, a fluidic logical device ofthree-dimensional-type is also known wherein the fluid control space ismade three-dimensional. According to this type, the phenomenon of thefluid attaching to the wall of the control chamber can be eliminated andit is considered that the device of this type can be used in anequipment wherein the control pressure or flow rate change is large.However, by employing such principle construction only of the fluidicdevice in a carburetor, it is impossible to produce economically acarburetor which will satisfy the flow control requirement over theentire operational range of engine.

As the reasons therefor, the following may be considered. Namely, incontrolling the flow rate by means of a fluidic device of the typewherein the control pressure varies continuously, the flow rate Qf offuel to be supplied to the engine varies generally in proportion to thecontrol negative pressure P as shown in FIG. 1. On the other hand, theflow rate Qf of fuel to be supplied to the engine must basically be inproportion to the flow rate Qa of suction air as represented by a curvea in FIG. 2. However, the Venturi negative pressure P,, of thecarburetor varies relative to the suction air quantity Qa, in therelation P I(Qa as shown in FIG. 3. Therefore, if the Venturi negativepressure P only is utilized as the control pres- 7 sure, there will bethe relation as represented by a curve b of FIG. 2, between Qa and Qf.Namely, with only one fluidic element, it is impossible to maintain asuitable relation between the suction air quantity and the fuel flowrate over the entire operational range of the engine, and it isnecessary to use a plurality of elements or to correct the relationshipbetween the air flow rate and the control pressure.

In the idling of an engine wherein the engine suction air quantity isrelatively small, it is practically difficult to precisely control thesuction air quantity. This is because, when the engine rpm. is small,the variation in the Venturi negative pressure relative to the flow rateof suction air is relatively large and hence the rotation of enginebecomes instable due to a fluctuation of fuel flow rate. This problemcannot be solved only by the manner in which the control negativepressure is taken.

The object of the present invention is, therefore, to provide at a lowcost a carburetor, capable of providing the characteristics requiredover the entire operational range of engine from a low speed operationto a high speed operation, by making use of the concept of fluidiclogical device controlled in a three-dimensional space. A characteristicfeature of the present invention resides in the fact that a fuel flowcontrolling portion utilizing a fluidic logical device is provided as athreedimensional air space which does not confine the flow of fuel, andvarious control pressures are acted in said air space. Anothercharacteristic feature of the invention resides in the fact that the lowspeed fuel line is partially composed of a line having no fluidiclogical element incorporated therein.

BRIEF DESCRIPTION OF THE DRAWINGS- FIG. -5 is a transversecross-sectional view taken on the line Y V-V of FIG. 4;

FIG. 6 is a diagram showing the relationship between the suction airquantity and the fuel flow rate in the carburetor of FIGS. 4 and 5; v

FIG. 7 is a diagram showing the characteristics of the carburetor ofFIGS. 4 and 5 as measured by mounting it on an actual engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT I A preferred embodiment of thepresent invention will be described hereinafter with reference to theaccompanying drawings. Referring to FIGS. 4 and 5, reference numeral Idesignates an air passage of the carburetor, in which suction air-flowsin the direction of the arrow, 2 a Venturi and 3 a throttle valve.Reference numeral 4 generally designates a fuel supply line forcirculating fuel therethrough, which is composed of a fuel supplypassage 5, a first fuel return passage 6, a

fuel tank 7 and a fuel pump 8. Reference numeral 9 designates a controlchamber formed interior of the carburetor body 10 and a nozzle 11communicating with the fuel supply passage 5 is projecting into theupper portion thereof. The .control chamber 9 may be formed in a controldevice provided separately from the carburetor body 10. Below the fuelnozzle 11 is provided a partition member 12 by which the lower portionof the control chamber 9 is divided into a fuel return reservoir 13 anda fuel supply reservoir 14. The fuel return reservoir 13 is incommunication with the fuel return passage 6, while the fuel supplyreservoir 14 is in communication with a fuel supply passage 15 which inturn is open into the Venturi 2. In the case where the control chamber 9is formed in a control device provided separately from the carburetorbody 10, said passage is communicated with air passage 1 of thecarburetor by suitable means.

On one side of and immediately below the fuel nozzle 1 l is provided avent nozzle 16 which projects into the control chamber 9 with the axisthereof extending substantially perpendicular to the axis of said fuelnozzle 11. Opposite to the vent nozzle 16 are provided a main controlnozzle 17 and an auxiliary control nozzle 18 which also project into thecontrol chamber 9 with the axes thereof extending substantiallyperpendicular to the axis of the fuel nozzle 11. It will be obvious thatthe axes of the respective nozzles are not necessarily in perpendicularrelation to each other but are only required to be in crossing relationor in adjacent relation within the control chamber 9. The vent nozzle 16is in communication with the air passage 1 at a point upstream of theVenturi 2, through a vent passage 19. On the other hand, the maincontrol nozzle 17 is in communication with the Venturi 2 through acontrol passage 20 and the auxiliary control nozzle 18 is communicatedthrough a low speed fuel passage 21 with an idle port 22, open into theair passage 1 at a point immediately downstream of the throttle valve 3,and with a by-pass port 23 open into the air passage 1 at a pointimmediately upstream of said throttle valve 3. The low speed fuelpassage 21 is further communicated with the fuel passage 5 through a lowspeed fuel passage 24. Reference numeral 25 designates a mainrestriction, 26 an idle restriction, 27 an auxiliary air restriction, 28an air bleed and 29 an idle adjusting screw. The fuel supply reservoir14 is also communicated with the fuel tank 7 through a second fuelreturn passage 30 to return a part of fuel to said fuel tank.

The degrees of projection into the control chamber 9, the diameters andthe relative position of the fuel nozzle 11, the vent nozzle 16 and themain and auxiliary control nozzles l7, 18 are preferably determinedthrough experiments. It is only important to select these factors suchthat the fuel will not be attached to the wall of the control chamber 9and the fuel flow rate can easily be controlled and further the fuelwill not be sucked from the main and auxiliary nozzles 17, 18.

The control chamber 9 may be rectangular in the cross-sectional shape,for example, as shown in FIG. 5 and the line of the top edge of thepartition member 12 may be straight as indicated by the chain line A.Alternatively, the line of the top edge of the partition member 12 maybe curved as indicated by the solid line B, as required.

With the construction described above, when the engine is not inoperation or, in other words, when there is no Venturi negativepressure, the fuel ejected from the fuel nozzle 11 flows into the fuelreturn reservoir 13 in its entirety due to the presence of the partitionmember 12 and returns to the fuel tank 7. When the engine has beenstarted, a negative pressure develops in the vicinity of the idle port22 and thence acts in the fuel passage 5 through the low speed fuelpassages 21 and 24. Therefore, the fuel flows into the low speed fuelpassage 21 from the fuel passage 5 through the low speed fuel passage 24and is mixed with the air sucked through the auxiliary control nozzle18. The resultant fuel-air mixture is supplied into the engine throughthe idle port 22 and the air passage 1. The negative pressure acting inthe auxiliary control nozzle 18 simultaneously causes an air flow fromthe vent nozzle 16 into said auxiliary control nozzle 18. This air flowcollides against the jet of fuel being ejected through the fuel nozzle11 and changes the direction of said jet of fuel, so that the jet offuel is divided by the partition member 12 into two fuel flows, one ofwhich is directed into the fuel supply reservoir 14 and supplied intothe air passage 1 through the main fuel passage 15. The ratio of thefuel supplied through the main fuel passage 15 to the total quantity ofthefuel supplied under such condition is about 50 percent or lower. Asstated, at the start and during idling of the engine, the quantity offuel supplied to the engine is controlled mainly by the low speed fuelpassage 21 which has a relatively stable fuel flow characteristic owingto the effect of the idle restriction 26, and, therefore, is stable evenif the negative pressure is fluctuated by the pulsation of enginesuction.

As the opening degree of the throttle valve 3 is increased slowly fromthe idling state, the negative pressure acting in the idle port 22becomes smaller but, on the other hand, a negative pressure begins toact in the by-pass port 23. Therefore, the quantity of fuel suppliedthrough the low speed fuel passage 24 will not decrease abruptly.

The increase in opening degree of the throttle valve 3 also results inthe increase of the negative pressure in the Venturi 2. This negativepressure acts to change the direction of the fuel jet through the maincontrol nozzle 17, with the result that the quantity of fuel flowinginto the fuel supply reservoir 14increases. Under such condition, theeffect of the engine suction pulsation, etc. is very minor and the fuelsupply quantity can be controlled by the negative pressure whichsubstantially corresponds to the quantity of suction air.

Since the respective nozzles project into the control chamber 9, thefuel is not allowed to attach on the wall of said chamber, nor is thefuel sucked from the main and auxiliary control nozzles 17,18. Further,the total quantity of the fuel supplied through the low speed fuelpassage 21 and the fuel supplied through the main fuel passage 15 can beincreased with the quantity of suction air of the engine increasing.

As stated previously, it is impossible, with the fluidic logical deviceonly, to maintain the fuel quantity basically in proportional relationto the increasing quantity of the suction air over a wide range of theengine operation. In the present invention, a fuel supply line for usein the low speed operation range of the engine is provided. Therefore,by suitably adjusting the relationship between the range within whichthe fuel supply line is used and the range within which the fluidicdevice operates, it is possible to obtain a suitable fuel flowcharacteristic over the range from the low speed operation to theintermediate speed operation of the engine. For obtaining a suitablefuel flow characteristic for the high speed operation range of theengine, a correction must be made andvarious methods can be consideredto effect such correction. One of the methods is to draw the line of thetop edge of the partition member 12 into a suitable configuration, e.g.into a curved line as indicated by B in FIG. 5, whereby the tendency ofthe fuel flow rate becoming excessively high in the high speed region ofthe engine can be inhibited. Another method is to provide a mainrestriction 25 in the main fuel passage 15 and return a part of the fuelto the fuel tank 7 through the second fuel return passage 30 which isopen into said main fuel passage 15 at a point upstream of said mainrestriction 25. In this case, the Venturi negative pressure acts in thedownstream of the main restriction 25 and this negative pressure becomeslarge as the fuel flow rate increases, so that the flow resistancecreated by said main restriction 25 increases and hence the ratio of thefuel entering the second return passage 30 increases.

The fuel flow characteristic may also be corrected by suitably selectingthe sizes of the vent nozzle 16 and the air bleed 28.

By employing these corrective means either singly or in combination, asuitable relationship between the fuel flow rate and the suction airquantity can be established over a wide operational range of the engine.

In the manner described, it is possible to supply fuel to the engine ina quantity proportional to the quantity of suction air within the rangefrom the start or idling state to the high speed operation of theengine.

Of course, the fuel flow characteristic required is not so simple asstated above and a correction to the concentration of the fuel-airmixture becomes necessary when the engine load becomes excessively largeor when the engine speed is to be accelerated or decelerated or when theengine is to be started at a low temperature. However, such correctioncan easily be made by changing the manner of imparting the controlpressure, as long as the basic relationship between the quantity ofsuction air and the quantity of fuel supplied to the engine isestablished.

In some types of engine, the fluctuation of the negative pressure in thesuction pipe is relatively small. In the case of such engines, only theVenturi negative pressure may be used as a control signal. It is also tobe understood that the by-pass line may occasionally be omitted, evenwhen the low speed fuel line is provided.

FIG. 6 exemplifies the relationship between the air flow rate Ga and thefuel flow rate Qf in a carburetor according to this invention. In thediagram of FIG. 6, the line a represents the relationship establishedwhen the fuel is supplied through the low speed fuel supply line, andthe line b represents the relationship established when the fuel issupplied through the main fuel supply line. The area 0 represents aportion of the fuel flow rate according to the line b which is correctedby the configuration of the line of the top edge of the partition member12, the main restriction 25, the secondary return passage 30 or the airbleed 28, and the line d represents the relationship established by thecarburetor as a whole. FIG. 7

shows the characteristic curve of a carburetor embodying the presentinvention, as measured by mounting it on an engine of 42 cc indisplacement. Such characteristic can readily be obtained by adjustingthe suction air flow rate vs. fuel flow rate relationship represented bythe line d in FIG. 6. It will be understood from the characteristiccurve that the air-fuel ratio is continuously decreased as the state ofthe engine is shifted from idling to a high speed operation.

As described above, according to the present invention it is possible toobtain a suitable air-fuel ratio from idling to a high speed operation,within the basic relationship between the air quantity and the fuelquantity to be supplied to the engine and without resorting to anymoving part. Therefore, the carburetor of the invention is highlyreliable in performance, very simple in construction as a whole and canbe produced at low costs.

What is claimed is:

1. A carburetor comprising a carburetor body, a control chamber formedeither integrally with or separately from said carburetor body, a fuelnozzle projecting into one end portion of said control chamber andconstituting an end portion of a fuel supply conduit communicating witha fuel tank, a partition member provided in the other end portion ofsaid control chamber in opposed relation to said fuel nozzle fordividing said portion into a fuel return reservoir and a fuel supplyreservoir, said fuel supply reservoir being in communication with aVenturi within the air passage of the carburetor through a main fuelpassage, a control nozzle projecting into said control chamber with itsaxis extending in crossing or adjacent relation to the axis of said fuelnozzle within said control chamber, an auxiliary control nozzleprojecting into said control chamber at a location closer to said fuelnozzle than said control male and a vent noule provided in said controlchamber at a location opposite to said control nozzle and auxiliarycontrol nozzle, said control nozzle being in communication with saidVenturi or a portion of the air passage in the proximity of saidVenturi, said auxiliary control nozzle being in communication with aportion of the air passage in the proximity of a throttle valve througha low speed fuel supply passage which is in communication with said fuelsupply conduit and said vent nozzle being in communication with aportion of the air passage where the atmospheric pressure or a pressureapproximate thereto will act.

2. A carburetor as defined in claim 1, wherein a main restriction isprovided in said main fuel passage and a fuel return passagecommunicating with the fuel tank is provided to open into said main fuelpassage at a location upstream of said main restriction.

3. A carburetor as defined in claim 1, wherein said low speed fuelpassage is communicated with an idle port which is open into the airpassage at a location immediately downstream of the throttle valve andwith a by-pass port which is open into said air passage at a locationimmediately upstream of said throttle valve, and an idle adjusting screwis provided in said low speed fuel passage.

4. A carburetor as defined in claim 1, wherein said control chamber isshaped into a rectangle or a shape similar thereto in cross-section andthe line of the top edge of said partition member is traced such thatthe area of the fuel supply reservoir projects into the area of the fuelreturn reservoir.

5. A carburetor as defined in claim 1, wherein an air bleed is providedin said main fuel passage.

1. A carburetor comprising a carburetor body, a control chamber formedeither integrally with or separately from said carburetor body, a fuelnozzle projecting into one end portion of said control chamber andconstituting an end portion of a fuel supply conduit communicating witha fuel tank, a partition member provided in the other end portion ofsaid control chamber in opposed relation to said fuel nozzle fordividing said portion into a fuel return reservoir and a fuel supplyreservoir, said fuel supply reservoir being in communication with aVenturi within the air passage of the carburetor through a main fuelpassage, a control nozzle projecting into said control chamber with itsaxis extending in crossing or adjacent relation to the axis of said fuelnozzle within said control chamber, an auxiliary control nozzleprojecting into said control chamber at a location closer to said fuelnozzle than said coNtrol nozzle and a vent nozzle provided in saidcontrol chamber at a location opposite to said control nozzle andauxiliary control nozzle, said control nozzle being in communicationwith said Venturi or a portion of the air passage in the proximity ofsaid Venturi, said auxiliary control nozzle being in communication witha portion of the air passage in the proximity of a throttle valvethrough a low speed fuel supply passage which is in communication withsaid fuel supply conduit and said vent nozzle being in communicationwith a portion of the air passage where the atmospheric pressure or apressure approximate thereto will act.
 2. A carburetor as defined inclaim 1, wherein a main restriction is provided in said main fuelpassage and a fuel return passage communicating with the fuel tank isprovided to open into said main fuel passage at a location upstream ofsaid main restriction.
 3. A carburetor as defined in claim 1, whereinsaid low speed fuel passage is communicated with an idle port which isopen into the air passage at a location immediately downstream of thethrottle valve and with a by-pass port which is open into said airpassage at a location immediately upstream of said throttle valve, andan idle adjusting screw is provided in said low speed fuel passage.
 4. Acarburetor as defined in claim 1, wherein said control chamber is shapedinto a rectangle or a shape similar thereto in cross-section and theline of the top edge of said partition member is traced such that thearea of the fuel supply reservoir projects into the area of the fuelreturn reservoir.
 5. A carburetor as defined in claim 1, wherein an airbleed is provided in said main fuel passage.